Thermally Induced Spin Transitions in Nitroxide−Copper(II)−Nitroxide Spin Triads Studied by EPR

Fedin, Matvey V.; Veber, Sergey L.; Gromov, Igor; Maryunina, Kseniya; Fokin, S. V.; Романенко, Г. В.; Sagdeev, R. Z.; Овчаренко, В. И.; Bagryanskaya, Elena G.

doi:10.1021/ic7014385

Cited by 57 publications

(121 citation statements)

References 36 publications

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“…21,61,[72][73][74][75][76][77][78][79][80][81][82][83] The specific characteristics originate from predominant population of ground spin multiplet 72 and dynamic mixing (electron spin exchange) processes. 73 EPR of these compounds complements the magnetic susceptibility and X-ray techniques, and represents an efficient method for studying exchange interactions and coordination modes.…”

Section: Epr Study Of Breathing Crystalsmentioning

confidence: 99%

“…The main features of the EPR spectra of nitroxide-copper-nitroxide three-spin systems exchange-coupled with |J| > kT were studied in 72,74,80 and are summarized below. As has been mentioned above, structural rearrangements in octahedral units CuO 6 at lower temperatures lead to a significant shortening or lengthening of the Cu-O distances 11 and, consequently, to the changes of the exchange-interaction magnitude ( Fig.…”

Section: Transitionsmentioning

confidence: 99%

“…74 The manifestations of spin-transitions in both magnetic susceptibility and EPR data can be understood using a simple phenomenological model, 74 where the dependencies of the effective magnetic moment μ eff and the effective g factor of a spin-triad g eff are considered as functions of the parameter |J(T)|/kT. The effective magnetic moment of a spin-triad can be calculated as: E I are the energies of the corresponding multiplets.…”

Section: Classification Of Spin-transitions In Breathing Crystals Andmentioning

confidence: 99%

“…Reasonable values g Cu = 2.15 (isotropic value) and g R = 2.007 lead to g A = 1.96, g B = 2.15, and g C = 2.05, and thus μ eff = 3.077 β for |J|/kT ∼ 0 and μ tr , eff = 1.697 β for |J|/kT = 1, J < 0. 74 If |J|/kT < 1, all of the total spin states of a triad (two doublets and one quartet) are almost equally populated, but if |J|/kT > 1, the ground state becomes predominately populated. Thus, the passage between situations |J|/kT < 1 and |J|/kT > 1 leads to the changes in the effective magnetic moment value and in the EPR spectra.…”

Section: Classification Of Spin-transitions In Breathing Crystals Andmentioning

confidence: 99%

“…Note that the amplitude of the spin transition is directly linked to the scale of the exchange-interaction and its change, as is clear from Eqs 9.5 and 9.8. 74 This simple phenomenological model and the approach described above were successfully used for the analysis of the different types of spin-transitions in breathing crystals. 74 Let's consider three examples with different characters of spin-transitions.…”

Section: Classification Of Spin-transitions In Breathing Crystals Andmentioning

confidence: 99%

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Breathing Crystals from Copper Nitroxyl Complexes

Овчаренко

Bagryanskaya

2013

Spin‐Crossover Materials

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IntroductionCoordination chemistry of transition metals with stable nitroxides is one of the actively developed branches of modern chemistry which is an important tool in solving the problems of molecular magnetism. The results of studies of metal complexes with nitroxides and their synthesis have been reported from various viewpoints in monographs and reviews. 1-19 Studies of heterospin compounds have led to the creation of new classes of compounds with new combinations of physical characteristics. 19 These include breathing crystals based on Cu(II) coordination compounds with stable nitroxides. Interest in these compounds has recently developed enormously and their number has increased dramatically. This prompted us to summarize data on their magnetostructural correlations. The discussion concentrated on Cu(II) hexafluoroacetylacetonate complexes [Cu(hfac) 2 ] with pyrazolyl-substituted nitronyl nitroxides. These compounds have been studied for more than 10 years 20, 21 and are well defined. The first part of the chapter summarizes the main features of breathing crystals, obtained using X-ray and magnetic measurements, and the second part overviews the results of EPR. EPR spectroscopy as applied to breathing crystals has a number of peculiarities which demands the development of new approaches. EPR study of breathing crystals is very informative, even though the exchange interaction in nitroxide-copper-nitroxide clusters significantly exceeds the value of Zeeman interaction.A very interesting characteristic of the complexes is the similarity of their magnetic properties to spintransitions in classical systems based on the temperature dependence of the effective magnetic moment (μ eff ). Note that the classical spin-crossover 22-35 is absolutely impossible in Cu(II) complexes with diamagnetic ligands, which contain only d 9 paramagnetic centers. The main distinction of spin-transitions in Cu(II) Spin-Crossover Materials: Properties and Applications, First Edition. Edited by Malcolm A. Halcrow.

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Section: Epr Study Of Breathing Crystalsmentioning

confidence: 99%

Section: Transitionsmentioning

confidence: 99%

Section: Classification Of Spin-transitions In Breathing Crystals Andmentioning

confidence: 99%

Section: Classification Of Spin-transitions In Breathing Crystals Andmentioning

confidence: 99%

Section: Classification Of Spin-transitions In Breathing Crystals Andmentioning

confidence: 99%

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Breathing Crystals from Copper Nitroxyl Complexes

Овчаренко

Bagryanskaya

2013

Spin‐Crossover Materials

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Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Овчаренко¹

2010

Stable Radicals

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IntroductionInteractions between the paramagnetic ions of transition metals and stable radicals are convenient and effective methods for the synthesis of multispin molecules. These metal-nitroxide systems are often called heterospin systems because they contain paramagnetic centers with both d (or f) odd electrons and centers with p electrons. Paramagnetic centers can differ in the electron spin, g factor, the character of electron spin density delocalization, and heat capacity. The presence of several paramagnetic centers in heterospin molecules has stirred growing interest in their magnetic properties because these compounds are convenient objects for studying the subtle peculiarities of exchange interactions and revealing valuable magnetostructural correlations. That is why coordination chemistry of transition metals with stable nitroxides is an actively developing direction in modern chemistry that contributes to problem solving in the field of molecular magnetism. The results of studies on the synthesis and properties of metal complexes with nitroxides have been considered from different viewpoints and at different times in many monographs and reviews. 1 -19 Importantly, this approach offers the potential for control over the structure of the designed heterospin molecule and the character of interactions between the odd electrons of paramagnetic centers, which is necessary for constructing justifiable magnetostructural correlations. This is one of the factors responsible for the continuous growth of the number of new metal-nitroxide complexes. The Cambridge Structural Database alone contains more than one thousand structurally defined metal-nitroxide systems. 20 Therefore, currently it is impossible and not necessary to collect all available literature data on the synthesis and properties of metal-nitroxide systems in one publication. In any account, a comprehensive review of this kind will already have become incomplete by the time of its publication because new heterospin compounds based on transition metal compounds with nitroxides are being added daily to the list. However, the Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron CompoundsEdited by Robin G. Hicks

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Light‐Induced Excited Spin State Trapping in an Exchange‐Coupled Nitroxide‐Copper(II)‐Nitroxide Cluster

et al. 2008

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The discovery of light-induced excited spin state trapping (LIESST) on a spin-crossover complex of iron(II) in 1984 attracted much attention in the field of photomagnetism and triggered a large number of subsequent studies. [1] Apart from being an interesting photophysical phenomenon, LIESST is one of the most promising effects for potential applications in molecular-level light-operated magnetic devices, because the metastable multiplet state excited by light may be trapped for hours to days at sufficiently low temperatures (typically below T c % 50 K). [1] Recent research on LIESST has been aimed at increasing the blocking temperature T c and expanding the range of compounds exhibiting this effect. To date, LIESST has been observed on compounds containing spin-crossover complexes of iron(II) and, more recently, iron(III). [2, 1i] In all of these cases, including exchange-coupled dinuclear complexes, [3] LIESST is based on the spin-crossover nature of iron. Herein, we report the first example of a LIESST-like effect observed in a system of principally different type, that is, an exchange cluster of copper(II) with two nitronyl nitroxide ligands. This compound does not contain any metals displaying spin crossover, and an efficient trapping of the light-induced state of a cluster on a timescale of hours originates from highly cooperative structural rearrangements in a one-dimensional system. Photoswitching of the exchange interaction has been studied in other one-dimensional systems aiming at ultrafast switching times. [4] In contrast, the present system shows a behavior more similar to the LIESST effect in iron compounds and is characterized by a long lifetime of the photoinduced state. Our finding introduces a new class of photoswitchable compounds and thus broadens the scope and range of potential applications of such systems.The polymeric complex [Cu(hfac) 2 L Pr ] (Figure 1) belongs to the family of so-called "breathing crystals" that we have studied extensively over the last few years. [5, 6] Breathing crystals [Cu(hfac) 2 L R ] have been found to exhibit thermally induced structural rearrangements accompanied by magnetic anomalies that are, in many respects, similar to a classical spin crossover (Figure 1). During these reversible rearrangements, the elongated (Jahn-Teller) axis of the octahedron is rotated, and the exchange interaction J in a spin triad between copper(II) and the nitroxide spins changes by up to one order of magnitude owing to the shortening or lengthening of interspin distances. [6d] This situation results in a change of the magnetic moment (i.e. spin transition), since at high temperatures the spins are weakly coupled (j J j ! kT, referred to as the weakly coupled spin (WS) state), whereas at low temperatures strong antiferromagnetic exchange effectively couples two of the three spins (j J j @ kT), and thus the spin triad converts to the strongly coupled spin (SS) state. We have found that EPR spectroscopy of breathing crystals allows us to monitor the spin transitions between WS a...

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Thermally Induced Spin Transitions in Nitroxide−Copper(II)−Nitroxide Spin Triads Studied by EPR

Cited by 57 publications

References 36 publications

Breathing Crystals from Copper Nitroxyl Complexes

Breathing Crystals from Copper Nitroxyl Complexes

Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Light‐Induced Excited Spin State Trapping in an Exchange‐Coupled Nitroxide‐Copper(II)‐Nitroxide Cluster

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